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+\documentclass{article}
+\usepackage{axiom}
+\begin{document}
+\title{\$SPAD/src/input tetra.input}
+\author{The Axiom Team}
+\maketitle
+\begin{abstract}
+\end{abstract}
+\eject
+\tableofcontents
+\eject
+\section{License}
+<<license>>=
+--Copyright The Numerical Algorithms Group Limited 1994.
+@
+<<*>>=
+<<license>>
+-- Sierpinsky's Tetrahedron
+
+-- Bring DH matrices into the environment
+)set expose add con DenavitHartenbergMatrix
+
+)read dhtri
+
+-- set up the coordinates of the corners of a tetrahedron
+x1:DoubleFloat := sqrt(2.0@DoubleFloat/3.0@DoubleFloat)
+x2:DoubleFloat := sqrt(3.0@DoubleFloat)/6
+
+p1 := point [-0.5@DoubleFloat, -x2, 0.0@DoubleFloat]
+p2 := point [0.5@DoubleFloat, -x2, 0.0@DoubleFloat]
+p3 := point [0.0@DoubleFloat, 2*x2, 0.0@DoubleFloat]
+p4 := point [0.0@DoubleFloat, 0.0@DoubleFloat, x1]
+
+-- The base of the tetrahedron
+baseTriangle  := [p2, p1, p3]
+
+-- The "middle triangle" inscribed in the base of the tetrahedon
+mt  := [0.5@DoubleFloat*(p2+p1), 0.5@DoubleFloat*(p1+p3), 0.5@DoubleFloat*(p3+p2)]
+
+-- The bases of the triangles of the subdivided tetrahedon
+bt1 := [mt.1, p1, mt.2]
+bt2 := [p2, mt.1, mt.3]
+bt3 := [mt.2, p3, mt.3]
+bt4 := [0.5@DoubleFloat*(p2+p4), 0.5@DoubleFloat*(p1+p4), 0.5@DoubleFloat*(p3+p4)]
+
+-- create the transformations which bring the base of the tetrahedron
+-- to the bases of the subdivided tetrahedron
+tt1 := tri2tri(baseTriangle, bt1)
+tt2 := tri2tri(baseTriangle, bt2)
+tt3 := tri2tri(baseTriangle, bt3)
+tt4 := tri2tri(baseTriangle, bt4)
+
+-- Draw a Sierpinsky tetrahedron with n levels of recursive subdivision
+drawPyramid(n) ==
+  s := create3Space()$ThreeSpace DoubleFloat
+  dh := rotatex(0.0@DoubleFloat)
+  drawPyramidInner(s, n, dh)
+  makeViewport3D(s, "Sierpinsky Tetrahedron")$VIEW3D
+
+-- Recursively draw a Sierpinsky tetrahedron
+drawPyramidInner(s, n, dh) ==
+  n = 0 => makeTetrahedron(s, dh, n)
+  -- draw the 4 recursive pyramids
+  drawPyramidInner(s, n-1, dh * tt1)
+  drawPyramidInner(s, n-1, dh * tt2)
+  drawPyramidInner(s, n-1, dh * tt3)
+  drawPyramidInner(s, n-1, dh * tt4)
+
+-- draw a tetrahedron into the given space, with the given color,
+-- transforming it by the given DH matrix
+makeTetrahedron(sp, dh, color) ==
+  w1 := dh*p1
+  w2 := dh*p2
+  w3 := dh*p3
+  w4 := dh*p4
+  polygon(sp, [w1, w2, w4])
+  polygon(sp, [w1, w3, w4])
+  polygon(sp, [w2, w3, w4])
+  void()
+@
+\eject
+\begin{thebibliography}{99}
+\bibitem{1} nothing
+\end{thebibliography}
+\end{document}